Parts 1 and 2 of a series of four presentations that formed the basis of my short course on spatial audio for artists at the Music Department, Ionian University, Corfu, July 2008

1. Spatial Sound
Music Department, Ionian University, Corfu, July 2008
Presented by Richard Elen

2. What is Spatial Sound?
• Sound recording/reproduction intended to
create or recreate a sense of space, such as
the environment of a performance
• Using knowledge of human hearing to
localise sound sources in space
• Possibly in conjunction with a visual aspect
such as film, live performance, etc

3. What is a Soundfield?
• The sound around us in an acoustic space.
• The sound around us in a virtual space.
• The pattern of sound waves reaching our
ears that we perceive as an acoustic
environment, real or imaginary.

4. Experiencing Space
• Hearing allows identification of source
direction from all around including above/
below
• We can also perceive distance of sources
from the listener
• How is this done with just two ears?

5. Directional Cues
• Intensity of the same sound in each ear
• Left/right arrival times of sound at the ears
• Spectral differences due to pinnae,
shoulders, body masking – HRTF (Head
Related Transfer Functions)
• Visual cues, especially for front/back

6. Distance Cues
• The further away a source is,
• The quieter it is
• the less high frequencies
• the more reverberation/reflections
• What about ‘depth’

7. Environment Cues
• Relationship between direct and reflected
sound
• Character of early reflections
(where are the walls?)
• Character of reverberation/reverb time
(how big is the space?)

8. Spatial Sound:
Applications
• Capturing an acoustic event such as a live
performance more fully/accurately
• Mixing a multitrack recording to place
instruments around the listener
• Using computers to generate virtual
soundfields via algorithms
• Recreating those experiences at home or
in a performance environment

9. General vs
Special Solutions
• Yes, you can just put speakers anywhere
and play sounds through them.
• But you cannot reproduce/recreate a
soundfield.
• An overall technology offers repeatability
and a general solution rather than a special
one.

10. Questions
• “We are there” versus “They are here”
• How easy is it for the listener to experience
correctly?
• How do we integrate live performers?
• “Spatial accuracy” versus “immersion” →
• “Artistic Illusion” versus “Accurate 3D
rendering” →

11. Accuracy or Immersion
• Which is most important?
• Why?
• How much does it depend on the application?

12. Artistic Illusions?
• Live natural/acoustic music and spaces
• Multitrack-derived music
• Performance art
• Radio/TV sound (drama etc)
• Cinema sound

13. Accurate Rendering?
• Virtual Reality/Gaming
• Simulators and control systems
• Conferencing

14. From Mono to…
• Early equipment: monophonic.
Crude spatial cues via reverberation.
• Phonograph and Gramophone

15. Clement Ader
• Clement Ader made the first
stereo transmission

16. Clement Ader
• Pairs of mics
feeding pairs
of earphones
• From the
Paris Opera
to the 1881
Exhibition

17. Clement Ader
• Early binaural
but with
spaced mics

18. Bell Labs 1930s
• Attempted to recreate wavefronts at the
listener, using multiple mics/channels/
speakers
• Mainly aimed at cinema, not consumers
• Settled on three L-C-R mics/channels/
speakers, also tried two spaced omnis
• Also worked with 2 channels for disc

19. Blumlein 1930s
• 1903–1942
• Employed by EMI
• A true genius: Recording,
Television, Radar...
• Developed various stereo
technologies
• Coincident mics instead of
spaced ones

20. Blumlein Stereo I
• Crossed
figure-eights

21. Blumlein Stereo II
• “Mid-Side” (M-S)
• Coincident Omni and
figure-eight
• Delivers L+R (M)
and L-R (S)
• Matrixed to L & R

22. Other Stereo
Mic Systems
• A-B Stereo
Mics
• Spaced
Omnis

23. Other Stereo
Mic Systems
• XY Stereo:
Coincident
Cardioids

24. Other Stereo
Mic Systems
• ORTF stereo – spaced, wider cardioids

25. Binaural
(Dummy Head)
• Attempts to capture all
the information the
hearing system would
capture
• Technique passes in and
out of fashion
• Very effective at best

26. Binaural II
• Listen on headphones
(speakers require a
transfer function)
• Can be very good
indeed, but there are
problems
• DSP-synthesised
binaural mixing

27. Stereo Mixing I
• Localise sources between two speakers
using level alone
• Effect depends on listener position
• Standard technique for multitrack mixing

28. Stereo Mixing II
• Level-only panning
makes listener
position important

29. Consumer Stereo
• 1950s: Stereo Vinyl discs using Blumlein’s
cutting technique
• Classical music with various mic techniques
• Popular music mixed from multitrack

30. Cinema Stereo
• Multichannel effects used for Fantasia
(1939): 3 audio channels with a control
track; several speakers including rear.
• Otherwise mono until 1950s
• Initially, stereo music and panned dialogue
• Later, mono dialogue (listener position and
production problems)

31. Cinema Sound
• 1960s: 70mm presentations with multiple
front channels, one surround channel and
LFE/Sub
• Origin of current cinema surround systems

32. Quadraphony I
• 1970s: A first attempt at surround sound
for the consumer market
• Need for compatibility with stereo discs
• ‘Discrete’ 4-channel plus several
incompatible matrixes: SQ, QS, RM, CD-4,
UD-4...
• None worked very well

33. Quadraphony II
• ‘Discrete’ quad: four channels each feed a
speaker – LF, RF, LS, RS ‘Quadrifontal’ (‘four
source’) approach based on extending
panpotted stereo into two dimensions
• Level-only panning between 4 corners of a
square
• Speakers wider than normal stereo (90°
instead of 60° – hole in the middle)

34. Quadraphony III
• Fundamental flaws in localisation
approach
• Level-only panning works poorly
at the back, almost non-existent
at sides
• ‘Discrete’ quad was a failure:
matrix quad even more so

35. Quadraphony IV
• Three types of
Quad transmission
system:
• Discrete
• Subcarrier disc
• Matrix disc

36. Quadraphony IV
• Systems did not
accurately reproduce
the localisation intent
• UD-4 nearly got it
right

37. The roots of 5.1
• Matrix Quad formed the basis of Dolby
Surround
• ‘Steering’/ ‘logic’ circuits to make it appear
that separation was sufficient.
• Still a 2-channel matrix system

38. Cinema Surround
• Analogue cinema systems:
• Left & Right Front
• Added Centre Front for Dialogue
(due to poor audibility)
• One Surround channel for envelopment,
spaciousness
• Low Frequency Effects (LFE)

39. Movie Surround
• Advent of digital systems allowed more
channels
• LF, CF, RF at the front;
• LS, RS at the rear
• LFE
• This is ‘5.1’

40. L, C, R, Ls, Rs
‘5.1’ N
C
• Front L & R
L R
speakers are at 30º
normal stereo 100–120º
positions
• CF for dialogue Ls Rs
• Surround L & R are
very far apart

41. ‘5.1’ N
C
• Surrounds may L R
also be along the 30º
sides (eg cinema)
100–120º
• What do the
speaker positions tell
us about the intent Ls Rs
of 5.1 – and cinema
surround?

42. ‘5.1’ N
C
• 5.1 is designed L R
for envelopment 30º
and impressive
effects, not for 100–120º
localisation
accuracy Ls Rs
• Envelopment vs
localisation

43. An important aside:
Bass Management
• Misunderstanding the difference between
the LFE and the Subwoofer
• Bass management ensures that bass is
played by speakers that can handle it.
• There is no need for an LFE in music (or
anything else)
• Errors here can seriously affect replay!

44. Bass Management
• Never connect the LFE to the subwoofer:
in the studio or at home
• The LFE is not the ‘subwoofer channel’!
• Never send signals direct to the LFE
• Play safe and do not use the LFE at all!

45. Beyond 5.1
• All these systems are descendants of
‘discrete quad’
• One channel to one speaker
• Using more channels/speakers to fill in the
holes.
• 7.1... 10.2... 20.4... where will it end?

46. Audio Rendering:
a different approach
• Capture or create the soundfield in the
most effective way
• Transmit/store it in the most efficient way
• Replay it the best the system can do
• Analogous to a Postscript file/printer
• ‘Device-independent audio’